The encapsulation of various biological materials in biologically compatible materials, which is well documented in the literature, is a technique that has been used for some time, albeit with limited success. Exemplary of the art are U.S. Pat. No. 5,227,298 (Weber, et al.); U.S. Pat. No. 5,053,332 (Cook, et al.); U.S. Pat. No. 4,997,443 (Walthall, et al.); U.S. Pat. No. 4,971,833 (Larsson, et al.); U.S. Pat. No. 4,902,295 (Walthall, et al.); U.S. Pat. No. 4,798,786 (Tice, et al.); U.S. Pat. No. 4,673,566 (Goosen, et al.); U.S. Pat. No. 4,647,536 (Mosbach, et al.); U.S. Pat. No. 4,409,331 (Lim); U.S. Pat. No. 4,392,909 (Lim); U.S. Pat. No. 4,352,883 (Lim); and U.S. Pat. No. 4,663,286 (Tsang, et al.). Also of note is U.S. Pat. No. 5,643,569 to Jain, et al., incorporated by reference herein. Jain, et al. discuss, in some detail, the encapsulation of islets in various biocompatible materials. Islets produce insulin, and the use of the materials disclosed by Jain, et al. in the treatment of diabetes is taught therein.
The Jain, et al. patent discusses, in some detail, the prior approaches taken by the art in transplantation therapy. These are summarized herein as well.
Five major approaches to protecting the transplanted tissue from the host's immune response are known. All involve attempts to isolate the transplanted tissue from the host's immune system. The immunoisolation techniques used to date include: extravascular diffusion chambers, intravascular diffusion chambers, intravascular ultrafiltration chambers, microencapsulation, and macroencapsulation. There are many problems associated with methods of the prior art, including a host fibrotic response to the implant material, instability of the implant material, limited nutrient diffusion across semi-permeable membranes, secretagogue and product permeability, and diffusion lag-time across semi-permeable membrane barriers.
For example, a microencapsulation procedure for enclosing viable cells, tissues, and other labile membranes within a semipermeable membrane was developed by Lim in 1978. (Lim, Research report to Damon Corporation (1978)). Lim used microcapsules of alginate and poly L-lysine to encapsulate islets of Langerhans (referred to as "Islets" hereafter). In 1980, the first successful in vivo application of this novel technique in diabetes research was reported (Lim, et al., Science 210: 908 (1980)). The implantation of these microencapsulated islets resulted in sustaining a euglycemic state in diabetic animals. Other investigators, however, repeating these experiments, found the alginate to cause a tissue reaction and were unable to reproduce Lim, et al.'s results (Lamberti, et al. Applied Biochemistry and Biotechnology 10: 101 (1984); Dupuy, et al., J. Biomed. Material and Res. 22: 1061 (1988); Weber, et al., Transplantation 49: 396 (1990); and Doon-shiong, et al., Transplantation Proceedings 22: 754 (1990)). The water solubility of these polymers is now considered to be responsible for the limited stability and biocompatibility of these microcapsules in vivo (Dupuy, et al., supra, Weber et al., supra, Doon-shiong, et al., supra, and Smidsrod, Faraday Discussion of Chemical Society 57: 263 (1974)).
Iwata et al., (Iwata, et al. Jour. Biomedical Material and Res. 26: 967 (1992)) utilized agarose for microencapsulation of allogeneic pancreatic islets and discovered that it could be used as a medium for the preparation of microbeads. In their study, 1500-2000 islets were microencapsulated individually in 5% agarose and implanted into streptozotocin-induced diabetic mice. The graft survived for a long period of time, and the recipients maintained normoglycemia indefinitely.
Their method, however, suffers from a number of drawbacks. It is cumbersome and inaccurate. For example, many beads remain partially coated and several hundred beads of empty agarose form. Additional time is thus required to separate encapsulated islets from empty beads. Moreover, most of the implanted microbeads gather in the pelvic cavity, and a large number of islets in completely coated individual beads are required to achieve normoglycemia. Furthermore, the transplanted beads are difficult to retrieve, tend to be fragile, and release islets easily upon slight damage.
A macroencapsulation procedure has also been tested. Macrocapsules of various different materials, such as poly-2-hydroxyethyl-methacrylate, polyvinylchloride-c-acrylic acid, and cellulose acetate were made for the immunoisolation of islets. (See Altman, et al., Diabetes 35: 625 (1986); Altman, et al., Transplantation: American Society of Artificial Internal Organs 30: 382 (1984); Ronel, et al., Jour. Biomedical Material Research 17: 855 (1983); Klomp, et al., Jour. Biomedical Material Research 17: 865-871 (1983)). In all these studies, only a transitory normalization of glycemia was achieved.
Archer, et al., Journal of Surgical Research 28: 77 (1980), used acrylic copolymer hollow fibers to temporarily prevent rejection of islet xenografts. They reported long-term survival of dispersed neonatal murine pancreatic grafts in hollow fibers which were transplanted into diabetic hamsters. Recently Lacy, et al., Science 254: 1782-1784 (1991) confirmed their results, but found the euglycemic state to be a transient phase. They found that when the islets are injected into the fiber, they aggregate within the hollow tube with resultant necrosis in the central portion of the islet masses. The central necrosis precluded prolongation of the graft. To solve this problem, they used alginate to disperse the islets in the fiber. However, this experiment has not been repeated extensively. Therefore, the membrane's function as an islet transplantation medium in humans is questionable.
The Jain, et al. patent discussed supra reports that encapsulating secretory cells in a permeable, hydrophilic gel material results in a functional, non-immunogenic material, that can be transplanted into animals, can be stored for long lengths of time, and is therapeutically useful in vivo. The macroencapsulation of the secretory cells provided a more effective and manageable technique for secretory cell transplantation.
The patent does not discuss at any length the incorporation of cancer cells. A survey of the literature on encapsulation of cells reveals that, following encapsulation, cells almost always produce less of materials than they produce when not encapsulated. See Lloyd-George, et al., Biomat. Art. Cells & Immob. Biotech. 21(3): 323-333 (1993); Schinstine, et al., Cell Transplant 4(1): 93-102 (1995); Chicheportiche, et al., Diabetologica 31:54-57 (1988); Jaeger, et al., Progress In Brain Research 82:41-46 (1990); Zekorn, et al., Diabetologica 29:99-106 (1992); Zhou, et al., Am. J. Physiol. 274: C1356-1362 (1998); Darquy, et al., Diabetologica 28:776-780 (1985); Tse, et al., Biotech. & Bioeng. 51:271-280 (1996); Jaeger, et al., J. Neurol. 21:469-480 (1992); Hortelano, et al., Blood 87(12): 5095-5103 (1996); Gardiner, et al., Transp. Proc. 29:2019-2020 (1997). None of these references deal with the incorporation of cancer cells into a structure which entraps them and restricts their growth, but nonetheless permit diffusion of materials into and out of the structure.
One theory relating to the growth of cancerous masses likens such masses, e.g., tumors, to normal organs. Healthy organs, e.g. the liver, grow to a particular size, and then grow no larger; however, if a portion of the liver is removed, it will regenerate to a certain extent. This phenomenon is also observed with tumors. To summarize, it has been noted that, if a portion of a tumor is removed, the cells in the remaining portion of the tumor will begin to proliferate very rapidly until the resulting tumor reaches a particular size, after which proliferation slows down, or ceases. This suggests that there is some internal regulation of cancer cells.